This ppt is a brief description of 3 plane crashes hich have shaken the aviation industry

1. AVIATION DISASTERS DUE TO MECHANICAL FAILURES Seminar by Cyril Sudip 1NT05ME017

3. Aircraft Accident Report 1 Aloha Airlines 243 Boeing 737-200 Explosive decompression caused by metal fatigue Fatalities 1 Injuries 65 28 th April,1988

7. FUSELAGE - A BREATHING STRUCTURE LOW ALTITUTE, HIGH OUTSIDE PRESSURE HIGH ALTITUTE, LOW OUTSIDE PRESSURE It is estimated that an avg jet liner must support 5000 kg of force per sq. m

9. FAIL-SAFE DESIGN The fail safe design established by Boeing required that the fuselage be able to withstand a 40-inch crack without suffering a catastrophic failure. In previous fatigue evaluations,there was no consideration given to the joining of adjacent cracks Boeings design included the placement of tear straps with 10 inch spacing in the fuselage skin to redirect running cracks from external damage.

11. Flight 261 was operating from Mexico to Washington with a stopover at SF Captain had flown approximately 17000 flight hours and first officer over 8000 hours. Both had a good record of flying. Two hours after take off from Mexico, pilots discuss a jammed stabilizer and request diversion to LA international airport. Later, a mechanic at maintenance (LAX) contacts pilots, asks them status of the alternate trim system the pilots indicated that there was no appreciable change on engaging it. Pilots continue to fight the plane, they try disengaging and then re-engaging the autopilot. Later ,the CVR records a “loud noise". Airplane begins final decent and crashes into Pacific

12. First Dive Cleared to 17,000 feet Extremely Loud Noise

16. Aircraft Accident Report 3 & 4 Boeing 737s Design flaw United Airlines 585 Uncontrolled descent,collision with terrain Colorado Springs,Colorado Airplane destroyed on impact 25 people killed March 3 rd ,1991 USAir 427 Uncontrolled descent,collision with terrain Pittsburgh,Pennsylvania Airplane destroyed on impact 132 people killed September 8 th ,1994

17. On arriving at the crash site,Investigators zero in on the PCU knowing that the crew had problems controlling the airplane. PCU performs like a cars steering, it uses hydraulic fluid to convert the movement of the pilots foot into pressure required to move the rudder. The heart of the PCU is the dual servo valve , it contains two slides which direct the flow of hydraulic fluid to the rudder.

18. DUAL SERVO VALVE NORMAL OPERATION

20. CONCLUSION The constant maintenance and repair of aircraft may seem like a trivial job but they can prove to be fatal if not done properly A missing screw can jeopardize the whole aircraft Lack of lubrication costed 88 lives, these are lessons the aviation industry learnt the hard way